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No engine builder here
nor jet boat person nor 460 bbf petson but what the heck, i’ll take a stab :) the ol’ trusty comp cams 280h 230/230 at .050” 110 lsa https://www.compcams.com/magnum-mari...d-429-460.html |
Is Clay Smith cams still around?
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The problem with jets, in regard to cam'ing, jet drive need high rpm to get the water flowing effectively. You end up with a high cruise rpm with a high vacuum. The engine doesn't work very hard, but it's inefficient.
Berkely impeller chart: https://cimg6.ibsrv.net/gimg/www.off...b72379d24d.jpg500 HP at 5400 rpm. That's if the A imp isn't already cut down to increase rpm.450 HP at 5200. Cam: HR mid 22x Int with a lower 23X Ex with 0.550" lifts. Your LSA requirement will be dictated by the undervalved the BBF heads, and the conpression ratio. Essentually, how hard it is to have the int and exh ports interact with pressures/flow. An example for large displacement vs cam duration: The 365 Mag BBC (454) crate engines of the day, had a 224° single pattern FT cam with 0.510"lift, & 115.5° LSA. Peaked out at 390 hp (crank) at 5200rpm. Large Rec Port heads and 8.6 CR. Bottom line, the more accurate info you can generate, the more accurate your custom and/or shelf cam. |
Can't help with the cam choice but a buddy of mine had a Carlson/460/Berkley combo. I drove it a few times. I can tell ya the jet doesn't bite much at all until you're over 3k RPM.
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Very good info...I will try to track down some more specs on things with the old man to hopefully narrow it down a little more. Thanks!
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Jones Cams Marine Cam Selection Sheet copy:
https://cimg1.ibsrv.net/gimg/www.off...a808276d5e.jpg https://cimg3.ibsrv.net/gimg/www.off...4fd6b358d7.jpg There's a drop down selection where it says 'Jet' for various drive systems. Where it speaks to seat pressure etc, that would/could be prescribed by the cam suggestion...unless required to work with what you have etc. Generally, when building an engine, you need to have the heads finalized and complete...to dictate everythkng else like pistons and dome requirements for intended CR etc. |
I told him he is kinda putting the cart before the horse trying to get a cam before having the heads done compression fully figured. I think he is finally listening and will update when I have some more nailed down info. Thanks!
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Originally Posted by BBYSTWY
(Post 4937028)
Trying to help my old man out and figured I would ask the brain trust...he is getting a motor together for his jet boat and he's not looking to break any speed records just has some wants so figured I'd see what you guys thought....
460 ford(yeah I know lol) Not a huge ford researcher so he said he's getting "the good" ford heads...apparently they have some castings that are pretty good from the factory I guess Stock bottom end with all new bearings and seals of course 2x4 tunnel ram and will be running my Holley 2x4 EFI setup that I just took off my boat with ignition control Full dry exhaust over the transom He wants to stay hydraulic roller and wants to go as big as he can since he's running dry exhaust Again not worried about ringing every single HP out of it just wants it to sound as mean as possible and whatever power he gets, he gets lol It's a 19-20 ft beisemeyer jet boat that he will just be tooling around in annoying people on inland lakes more than likely hahaha Thanks for the help! Gotta know compression ratio to pick a cam |
What boattrubador said ... knowing the compression is key especially when you already know it is going to be "low" i.e. 8.5:1
With static compression in that range, a gnarly cam plus a tunnel ram and the 460's generous intake ports will be *extremely* lazy at planing and cruising RPM unless he's got a pretty small impeller cut. |
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